1. Field of the Invention
The present application relates in general to oil and gas drilling operations, and in particular to an improved method and apparatus for monitoring the operating conditions of a downhole drill bit during drilling operations.
2. Description of the Prior Art
The oil and gas industry expends sizable sums to design cutting tools, such as downhole drill bits including rolling cone rock bits and fixed cutter bits, which have relatively long service lives, with relatively infrequent failure. In particular, considerable sums are expended to design and manufacture rolling cone rock bits and fixed cutter bits in a manner which minimizes the opportunity for catastrophic drill bit failure during drilling operations. The loss of a cone or cutter compacts during drilling operations can impede the drilling operations and necessitate rather expensive fishing operations. If the fishing operations fail, side track drilling operations must be performed in order to drill around the portion of the wellbore which includes the lost cones or compacts. Typically, during drilling operations, bits are pulled and replaced with new bits even though significant service could be obtained from the replaced bit. These premature replacements of downhole drill bits are expensive, since each trip out of the wellbore prolongs the overall drilling activity, and consumes considerable manpower, but are nevertheless done in order to avoid the far more disruptive and expensive fishing and side track drilling operations necessary if one or more cones or compacts are lost due to bit failure.
IN GENERAL: The present invention is directed to an improved method and apparatus for monitoring and recording of operating conditions of a downhole drill bit during drilling operations. The invention may be alternatively characterized as either (1) an improved downhole drill bit, or (2) a method of performing drilling operations in a borehole and monitoring at least one operating condition of a downhole drill bit during drilling operations in a wellbore, or (3) a method of manufacturing an improved downhole drill bit.
When characterized as an improved downhole drill bit, the present invention includes (1) an assembly including at least one bit body, (2) a coupling member formed at an upper portion of the assembly, (3) at least one operating condition sensor carried by the improved downhole drill bit for monitoring at least one operating condition during drilling operations, and (4) at least one electronic or semiconductor memory located in and carried by the assembly, for recording in memory data pertaining to the at least one operating condition.
The present invention may be characterized as in improved drill bit for use in drilling operations in a wellbore. The improved drill bit includes an number of components which cooperate. A bit body is provided which includes a plurality of bit heads, each supporting a rolling cone cutter. A coupling member is formed at an upper portion of the bit body. Preferably, but not necessarily, the coupling member comprises a threaded coupling for connecting the improved drill bit to a drillstring in a conventional pin-and-box threaded coupling. The improved drill bit may include either or both of a temperature sensor and a lubrication system sensor.
TEMPERATURE SENSING: For example, the improved drill bit includes at least one temperature sensor for monitoring at least one temperature condition of the improved drill bit during drilling operations. In accordance with this particular embodiment of the present invention, at least one temperature sensor cavity is formed in the bit body and adapted for receiving, carrying and locating at least one temperature sensor in a particular position relative to the bit body which is empirically determined to optimize temperature sensor discrimination. At least one electronic or semiconductor memory member is provided, and located in, and carried by the drill bit body, for recording in memory data obtained by the at least one temperature sensor.
In accordance with this embodiment of the present invention, the temperature sensor cavity is located in the bit body in a position which is empirically determined to optimize temperature sensor discrimination. More particularly, the temperature sensor cavity is located in the head bearing in a substantially medial position which is proximate to the centerline of the head bearing. More particularly, the temperature sensor cavity is provided in a medial position within the head bearing about its centerline between its base and the thrust face.
CONDUCTOR ROUTING: Conductors are provided to communicatively couple the electrical components carried by the improved rock bit. A plurality of wire pathways are formed in the plurality of bit legs in order to allow the conductors to be routed to the electrical components. In order to allow electrical connection between the components carried in the legs of the improved rock bit, a novel tri-tube assembly is provided. The tri-tube assembly includes a plurality of fluid-impermeable tube segments. Each of the fluid-impermeable tube segments is placed into communication with a wire pathway in one of the plurality of bit legs. The opposite ends of the fluid-impermeable tube segments are brought together at a connector. Conductors are routed through the fluid-impermeable tube segments to provide power to power-consuming electrical components and to pass data between the electrical components.
LUBRICATION MONITORING: The present invention can also be utilized to monitor the operating condition of the lubrication systems in an improved rock bit. In accordance with the present invention, a bit body is formed from a plurality of bit legs. Each of the plurality of bit legs include a head bearing, a rolling cone cutter coupled to the head bearing, a bearing assembly facilitating rotary movement of the rolling cone cutter relative to the bearing head, a lubrication system for providing lubricant to the bearing assembly, and an electrical sensor in communication with the lubrication of the lubrication system for monitoring at least one electrical property of the lubricant.
Additionally, a semiconductor member is carried by the bit body, and a sampling circuit is provided for developing digital samples from the sensor from the plurality of bit legs and for recording the digital samples in the semiconductor memory. In accordance with one embodiment of the present invention, the electrical sensor comprises a dielectric sensor which is preferably, but not necessarily, a capacitive electrical component. In accordance with the present invention, the capacitive electrical component is placed within the lubrication system to allow lubricant to lodge between the capacitor plates. As the lubricant degrades during use due to working shear, or if ingress of drilling fluid into the lubricating system occurs, the lubricant is altered in a manner which changes the dielectric constant of the lubricant. An increase in working shear will result in an increase in the dialectric constant of the lubricant. This change in the dielectric constant of the lubricant is detected utilizing the capacitive circuit component. The ingress of drilling fluid will also impact the dielectric permitivity of the lubricant and can also be detected utilizing the capacitive circuit element.
TRANSIENT-PRESSURE CHANGE COMMUNICATION SYSTEM: The embodiment of the improved drill bit which is described herein further includes a relatively simple downhole-to-surface communication system which is utilized to provide a warning signal to a surface location by generating transient or persistent pressure change within the wellbore. A transient pressure change may be generated utilizing an erodible ball. The erodible ball is secured in position within the improved drill bit utilizing a fastener system. The erodible ball is maintained in a predetermined position relative to a flow path which supplies drilling fluid to at least one bit nozzle carried by the improved drill bit. Once a predetermined operating condition is detected by a monitoring system carried by the improved drill bit (such as the temperature and lubrication monitoring systems described above), the fastener system is actuated to release the erodible ball into the flow path. The erodible ball passes down the flow path toward the bit nozzle, where it is caught by the bit nozzle and serves to at least partially and temporarily obstruct the flow of drilling fluid through the bit nozzle. In accordance with the present invention, the erodible ball preferably includes at least one flow port extending through at a least a portion of the erodible ball to allow drilling fluid to pass therethrough, and at least one circumferential groove formed over at least one portion of the erodible ball to allow drilling fluid to pass around the ball.
PERSISTENT PRESSURE CHANGE COMMUNICATION SYSTEM: A persistent pressure change, as opposed to a transient or temporary pressure change, may be generated utilizing an electrically-actuable valve which utilizes the pressure differential between the central bore of the drillstring and the annular region between the drillstring and the borehole. For example, allowing fluid communication between the annulus and the central bore will decrease the pressure of the drilling fluid within the central bore. In this particular embodiment, a port is provided between the exterior of the bit body and the flow paths within the bit body. An electrically-actuable xe2x80x9cvalvexe2x80x9d is provided to block flow until signalling is required. Preferably, the xe2x80x9cvalvexe2x80x9d includes a structural body which is secured into a flow blocking condition by a propellent material that is thermally actuable. An electrical element is carried in the structural element. When an open flow path is desired, a current is passed through the electrical element causing it to change from a solid state to a gaseous state. This allows the structural element to change shape, allowing fluid flow between the central bore and the annulus. This causes a slight pressure decrease in the drilling fluid which is carried in the central bore.
At least one pressure sensor can be located in an uphole location (such as a surface location) in order to detect the pressure change. In accordance with the embodiment of the present invention which utilizes transient pressure changes, the erodible ball is constructed to erode or dissolve under exposure to drilling fluid in a manner which provides a pressure change of a minimum time duration, in order to distinguish the pressure change from pressure changes which occur for other reasons during drilling operations.
DOWNHOLE ADAPTIVE CONTROL: The present invention may also be utilized to provide adaptive control of a drilling tool during drilling operations. The purpose of the adaptive control is to select one or more operating set points for the tool, to monitor sensor data including at least one sensor which determines the current condition of at least one controllable actuator member carried in the drilling tool or in the bottomhole assembly near the drilling tool which can be adjusted in response to command signals from a controller.